Radial piston pump for producing high fuel pressure internal combustion engines

ABSTRACT

The invention relates to a radial piston pump with a drive shaft supported in a pump housing and preferably with a number of pistons, each in its own cylinder chamber, arranged radially with regard to the drive shaft, and with a plate attached to the ends of these cylinders oriented toward the drive shaft, which plate has a blind hole in its center for receiving the end of the associated piston, wherein on its circumference, the piston has a groove into which a snap ring is inserted in order to fasten a plate retainer to the piston, which holds the plate on the piston, which is characterized in that at the rim of the blind hole in the plate, a cylindrical recess is produced, wherein the diameter of the cylindrical recess is dimensioned so that the play between the snap ring and the circumference of the cylindrical recess is smaller than the depth of the groove.

BACKGROUND OF THE INVENTION Field of the Invention

The invention relates to a radial piston pump for producing high fuelpressure in fuel injection systems of internal combustion engines,particularly in a common rail injection system, with a drive shaftsupported in a pump housing, which shaft is embodied eccentrically orhas cam-like projections in the circumference direction, and preferablywith a number of pistons, each in its own cylinder chamber, arrangedradially with regard to the drive shaft, and with a plate attached tothe ends of these cylinders oriented toward the drive shaft, which platehas a blind hole in its center which receives the end of the associatedpiston, and on its circumference, the piston has a groove into which asnap ring is inserted in order to fasten a plate retainer to the piston,which holds the plate on the piston.

With a partial filling of the cylinder chambers, the components of theradial piston pump that are exposed to high pressure undergo anextremely high amount of stress.

SUMMARY OF THE INVENTION

In accordance with the present invention a radial piston pump providedwhich can withstand the pressures of up to 2000 bar that occur with apartial filling of the cylinder chambers and nevertheless can be easilyand inexpensively manufactured.

In a radial piston pump for producing high fuel pressure in fuelinjection systems of internal combustion engines, in particular in acommon rail injection system, with a drive shaft supported in a pumphousing, which shaft is embodied eccentrically or has cam-likeprojections in the circumference direction, and preferably with a numberof pistons, each in its own cylinder chamber, arranged radially withregard to the drive shaft, and with a plate attached to the ends ofthese cylinders oriented toward the drive shaft, which plate has a blindhole in its center for receiving the end of the associated piston, andon its circumference, the piston has a groove into which a snap ring isinserted in order to fasten a plate retainer to the piston, which holdsthe plate on the a piston, the object of the invention is attained byvirtue of the fact that at the rim of the blind hole in the plate, acylindrical recess is produced, where the play between the snap ring andthe circumference of the cylindrical recess is smaller than the depth ofthe groove. The cylindrical recess is used to contain the snap ring, ormore precisely stated, to contain the part of the snap ring whichprotrudes from the groove. The dimensioning of the cylindrical recessaccording to the invention achieves the fact that the snap ring iscontained in captive fashion in its space. As a result, greater forcescan be transmitted than in conventional radial piston pumps.

One particular embodiment of the invention is characterized in that theradius of the groove is greater than the radius of the snap ring. Thisdimensioning of the groove and of the snap ring produces the advantagethat the snap ring always rests against the bottom of the groove and notagainst the edges of the groove. As a result, damage to the seat isprevented and the initial stress of the snap ring can be optimallyutilized. The initial stress of the snap ring can be increased byincreasing the thickness and diameter of the snap ring as well as thediameter of the groove.

Another particular embodiment of the invention is characterized in thatthe region of the plate retainer that rests against the snap ringexpands radial to the piston and is embodied as flat. As a result, thesnap ring can be seen better before the plate is inserted into the plateretainer. This results in the fact that installation is simplified anderrors are prevented in the assembly of the radial piston pump accordingto the invention. Consequently, valuable time can be saved and the goalof zero errors can be better attained.

Another particular embodiment of the invention is characterized in thata step is embodied on the plate retainer. The step is advantageouslyused to center a spring which is used to prestress the plate toward thedrive shaft.

Another particular embodiment of the invention is characterized in thaton its circumference, the plate has a groove which contains a securingring which rests against the plate retainer. The elastic securing ringproduces a frictional and consequently play-free connection between theplate retainer and the plate. This assures that the piston base remainsin contact with the plate during operation. During insertion of theplate into the plate retainer, the securing ring flexes so that theplate retainer can be embodied as rigid.

Another particular embodiment of the invention is characterized in thatsnap segments are embodied on the plate retainer, which rest against thecircumference of the plate. In comparison to the claws known from theprior art, the snap segments have the advantage that they are morestable as a result of their size. Furthermore, the snap segments of oneplate retainer do not interlock as easily with the snap segments ofother plate retainers during storage. This facilitates the installationof the plate retainers.

Another particular embodiment of the invention is characterized in thatthe ends of the snap segments are each bent slightly outwards. As aresult, the installation of the plate is advantageously simplifiedbecause during insertion of the plate into the plate retainer, the snapsegments that are bent slightly outwards automatically spread out.

Another particular embodiment of the invention is characterized in thatthe ends of the snap segments each have a bevel. This produces the sameeffect as the snap segments that are bent slightly outwards. Theinstallation of the plate is simplified.

Another particular embodiment of the invention is characterized in thata polygonal or cylindrical ring is disposed between the drive shaft andthe plate. The ring is used to transmit forces from the eccentricallyembodied drive shaft onto the plate. The ring is advantageouslysupported against the drive shaft in a sliding fashion. The ring can beembodied either cylindrically or with flattened places.

In general, the current invention has the advantage that the basicconcept of this invention can easily be used on existing radial pistonpumps. Generally, the component strength is increased, particularly at azero delivery in the intake stroke, without increasing the space of theradial piston pump.

BRIEF DESCRIPTION OF THE DRAWINGS

Other advantages, features, and details of the invention are describedin detail with specific reference with the drawings. In wich

FIG. 1 shows a piston and a plate of a conventional radial piston pump;

FIG. 2a, 2 b and 2 c show a piston and a plate of a radial piston pumpaccording to a first embodiment of the current invention;

FIG. 3 shows a piston and a plate of a radial piston pump according to asecond embodiment of the current invention;

FIG. 4 shows a piston and a plate of a radial piston pump according to athird embodiment of the current invention;

FIG. 5 shows an enlarged depiction of the snap ring in the cylindricalrecess; and

FIG. 6 shows an enlarged depiction of the snap ring in the groove.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to the drawings in detail; FIG. 1 shows a sectional viewthat portion only of a conventional radial piston pump for producinghigh fuel pressure in fuel injection systems of internal combustionengines. That relates to the current invention. The principal design ofa radial piston pump, for example from the German patent DE 42 16 988C2, is assumed to be known and is therefore only briefly describedbelow.

The radial piston pump according to the invention is particularly usedin common rail injection systems for fuel delivery in diesel engines. Inthis connection “common rail” means the same thing as “common line” or“common distributor rail”. In contrast to conventional high-pressureinjection systems in which the fuel is delivered to the individualcombustion chambers by means of separate lines, the fuel injectors incommon rail injection systems are supplied from a common line.

The radial piston pump, a detail of which is shown in FIG. 1, includes adrive shaft that is supported in a pump housing and has an eccentricallyembodied shaft section. A polygonal ring is provided on the eccentricshaft section and the shaft section can rotate in relation to this ring.The ring includes a number of flattened places that are offset from oneanother, each of which supports a piston 1. The pistons 1 are eachcontained so that they can move back and forth in a cylinder chamber 2in the radial direction in relation to the drive shaft.

As shown in FIG. 1, a plate 3 is fastened to the end of the piston 1oriented toward the drive shaft. The plate 3 is secured to theassociated piston 1 by means of a plate retainer 4, which is embodied asa cage or spring plate. In addition, the plate 3 is pressed against thering (not shown) by means of a spring 5. In order to prevent the plateretainer 4 from slipping off of the piston 1, a snap ring 6 is insertedinto a groove 7 of the piston 1.

FIG. 2 is divided into FIGS. 2a, 2 b, and 2 c. FIG. 2a shows a sectionof a radial piston pump according to the invention, which is similar tothe one depicted in FIG. 1 in terms of design. Thus for the sake ofsimplicity, parts which appear in both FIGS. are given the samereference numerals. FIG. 2b shows only the plate retainer from FIG. 2a.FIG. 2c shows a view of the plate retainer in the direction of the arrowA in FIG. 2a.

A plate 3 is affixed to the piston 1 shown in FIG. 1. The plate 3 issecured to the piston 1 by means of a plate retainer 4. To this end, asnap ring 6 is installed in a groove 7, which is provided on thecircumference of the piston 1. In addition, the plate retainer 4 ispressed against the snap ring 6 by means of the spring (5 as shown inFIG. 1).

The plate 3 has a blind hole bore 9 in the center, which receives oneend of the piston 1 with form-fitting engagement. The rim of the blindhole 9 is provided with a cylindrical recess 26. The cylindrical recess26 is used to contain that part of the snap ring 6 that protrudes fromthe groove 7.

FIG. 5 is an enlarged depiction of the snap ring 6 and the cylindricalrecess 26. The tolerances are selected according to the invention sothat the snap ring 6 is always disposed in the recess 26. Themeasurement 1 is designed so that even with an unfavorable tolerancesituation, is always smaller than the measurement 2. As a result, thesnap ring 6 is contained in the recess 26 in captive fashion and cannotslip off of the piston 1.

FIG. 6 is an enlarged depiction of the dimensioning of the snap ring 6and groove 7. The tolerances of the groove 7 and the snap ring 6 areselected so that the snap ring 6 always rests against the groove bottom60 and not against the edges 61, 62 of the groove 7. This preventsdamage to the seat. The wire diameter of the snap ring 6, the diameterof the snap ring 6, and the diameter of the groove are increased incomparison to the embodiment shown in FIG. 2. As a result, a higher snapring initial tension can be produced than in the embodiment according toFIG. 1.

In the radial piston pump shown in FIG. 2a, the region of the plateretainer 4 which rests against the piston 1 has the form of a round disk20, which extends radial to the piston 1. This results in the fact thatthe groove 7 can be looked into before the plate 3 is inserted into theplate retainer 4. The disk-shaped region 20 is adjoined by a step 21,which is embodied on the circumference of the round disk 20. The plate 3is equipped with a bevel 25, which is spaced apart from the step 21.

Three snap segments 22 extend from the step 20, parallel to the piston1. The ends 23 of the snap segments 22 first bend inward and then bendslightly outward. The bent-inward part of the snap segments 22 forms anannular chamber that is disposed inside the plate retainer 4 and servesto contain a collar 24, which is embodied on the plate 3. Thebent-outward end pieces 23 of the snap segments 22 facilitate theinsertion of the plate 3 into the plate retainer 4.

In the embodiment shown in FIG. 3, only a section of a piston 1 isshown, as in FIG. 2a. The end of the piston 1 is contained in a blindhole 9, which is let into the center of a plate 3. The plate 3 issecured to the piston 1 by means of a plate retainer 4. The plateretainer 4 is fastened to the piston 1 by means of a snap ring 6. Thesnap ring 6 is partially contained in a groove 7 of the piston 1 andpartially contained in a cylindrical recess 26 of the plate 3. The plateretainer 4 is a turned part in which a step 21 is embodied. A continuouscollar 32 extends from the step 21, parallel to the piston 1. The rim ofthe collar 32 of the plate retainer 4 is provided with a bevel 40, whichfacilitates the installation of the plate 3.

A groove 30 is let into the circumference of the round plate 3 andcontains a securing ring 31. The securing ring 31 is embodied asresilient and can be pressed into the groove 30 during installation ofthe plate 3. This has the advantage that the plate retainer 4 can beprovided with the continuous collar 32 and can be embodied as rigid.

In contrast to the embodiment shown in FIG. 3, in the section of anotherembodiment of the radial piston pump according to the invention shown inFIG. 4, the plate retainer 4 is embodied as a deep-drawn part withrounded edges. In addition, the rim of the collar 32 of the plateretainer 4, as shown in the embodiment in FIG. 3, is provided with abevel 40 which facilitates the installation of the plate 3.

The radial piston pump, of which only parts are shown in FIGS. 1 to 6,is used to exert high pressure on a fuel that is supplied from a tank bya presupply pump. The highly pressurized fuel is then fed into thecommon distributor rail mentioned above.

The foregoing relates to preferred exemplary embodiments of theinvention, it being understood that other variants and embodimentstherefore are possible within the spirit and scope of the invention, thelatter being defined by the appended claims.

We claim:
 1. A radial piston pump for producing high fuel pressure infuel injection systems of internal combustion engines, in particular ina common rail injection system, with a drive shaft supported in a pumphousing, which shaft is embodied eccentrically or has cam-likeprojections in the circumference direction, and preferably with a numberof pistons (1), each in its own cylinder chamber (2), arranged radiallywith regard to the drive shaft, and with a plate (3) attached to theends of these cylinders oriented toward the drive shaft, which plate (3)has a blind hole (9) in its center for receiving the end of theassociated piston (1), wherein on its circumference, the piston (1) hasa groove (7) into which a snap ring (6) is inserted in order to fasten aplate retainer (4) to the piston (1), which holds the plate (3) on thepiston (1), the improvement wherein at the rim of the blind hole (9) inthe plate (3), a cylindrical recess (26) is provided, the diameter ofsaid cylindrical recess (26) being dimensioned so that the play betweenthe snap ring (6) and the circumference of the cylindrical recess (26)is smaller than the depth of the groove (7).
 2. The radial piston pumpaccording to claim 1, wherein the radius of the groove (7) is greaterthan the wire radius of snap ring (6).
 3. The radial piston pumpaccording to claim 1, wherein the region (20) of the plate retainer (4)that rests against the snap ring (6) expands radial to the piston (1)and is embodied as flat.
 4. The radial piston pump according to claim 1,wherein a step (21) is embodied on the plate retainer (4), adjoining adisk-shaped region (20) radially on the outside.
 5. The radial pistonpump according to claim 1, wherein on its circumference, the plate (3)has a groove (30) into which a securing ring (31) is inserted, whichrests against the plate retainer (3).
 6. The radial piston pumpaccording to claim 1, wherein snap segments (22) are embodied on theplate retainer (3), said snap segments resting against the circumferenceof the plate (3).
 7. The radial piston pump according to claim 6,wherein the ends (23) of said snap segments (22) are each embodied asbent slightly outward.
 8. The radial piston pump according to claim 6,wherein the ends (40) of said snap segments (22) each have a bevel. 9.The radial piston pump according to claim 1, further comprising apolygonal or cylindrical ring disposed between the drive shaft and theplate (3).
 10. The radial piston pump according to claim 2, wherein theregion (20) of the plate retainer (4) that rests against the snap ring(6) expands radial to the piston (1) and is embodied as flat.
 11. Theradial piston pump according to claim 2, wherein a step (21) is embodiedon the plate retainer (4), adjoining a disk-shaped region (20) radiallyon the outside.
 12. The radial piston pump according to claim 3, whereina step (21) is embodied on the plate retainer (4), adjoining adisk-shaped region (20) radially on the outside.
 13. The radial pistonpump according to claim 2, wherein on its circumference, the plate (3)has a groove (30) into which a securing ring (31) is inserted, whichrests against the plate retainer (3).
 14. The radial piston pumpaccording to claim 3, wherein on its circumference, the plate (3) has agroove (30) into which a securing ring (31) is inserted, which restsagainst the plate retainer (3).
 15. The radial piston pump according toclaim 4, wherein on its circumference, the plate (3) has a groove (30)into which a securing ring (31) is inserted, which rests against theplate retainer (3).
 16. The radial piston pump according to claim 2,wherein snap segments (22) are embodied on the plate retainer (3), saidsnap segments resting against the circumference of the plate (3). 17.The radial piston pump according to claim 3, wherein snap segments (22)are embodied on the plate retainer (3), said snap segments restingagainst the circumference of the plate (3).
 18. The radial piston pumpaccording to claim 4, wherein snap segments (22) are embodied on theplate retainer (3), said snap segments resting against the circumferenceof the plate (3).
 19. The radial piston pump according to claim 2,further comprising a polygonal or cylindrical ring disposed between thedrive shaft and the plate (3).
 20. The radial piston pump according toclaim 3, wherein the region (20) of the plate retainer (4) that restsagainst the snap ring (6) expands radial to the piston (1) and isembodied as flat.
 21. The radial piston pump according to claim 4,wherein a step (21) is embodied on the plate retainer (4), adjoining adisk-shaped region (20) radially on the outside.
 22. The radial pistonpump according to claim 5, wherein a step (21) is embodied on the plateretainer (4), adjoining a disk-shaped region (20) radially on theoutside.
 23. The radial piston pump according to claim 6, wherein on itscircumference, the plate (3) has a groove (30) into which a securingring (31) is inserted, which rests against the plate retainer (3). 24.The radial piston pump according to claim 7, wherein on itscircumference, the plate (3) has a groove (30) into which a securingring (31) is inserted, which rests against the plate retainer (3). 25.The radial piston pump according to claim 8, wherein on itscircumference, the plate (3) has a groove (30) into which a securingring (31) is inserted, which rests against the plate retainer (3).